The present invention relates generally to a manner by which to synchronize a receiver to a transmitter operable in a radio communication system, such as a cellular communication system that utilizes a spread-spectrum communication scheme. More particularly, the present invention relates to a delay lock loop (DLL) circuit, and an associated method, that synchronizes the receiver to a signal transmitted to the receiver by the transmitter.
The DLL circuit is configurable alternately to be operated in an acquisition mode and a tracking mode. And, the delay lock loop circuit is operable irrespective of the amplitude of an input signal applied thereto. That is to say, the delay lock loop circuit is amplitude-independent. And, the circuit operates in a deterministic manner, irrespective of the signal levels of input signals applied thereto. Circuit-design compromises required in conventional delay lock loop circuits, due to the amplitude sensitivity of such conventional circuits are not required, thereby permitting simplified circuitry that does not require input-signal normalization for operation of the delay lock loop circuit.
A communication system operates to communicate data between two or more locations at which communication stations, operable in the communication system, are positioned. Data, sourced at a sending station, is communicated upon a communication channel to be terminated at a receiving station.
Many varied types of communication systems have been developed and communication of data through the use of such communication systems is a pervasive aspect of modern society. And, the need to communicate data shall likely become increasingly pervasive in the future.
Advancements in communication technologies are implemented into existing communication systems to improve their performance. And, advancements in communication technologies have permitted the implementation of new types of communication systems that provide for new types of communication services, previously unavailable.
A radio communication system is an exemplary communication system and is exemplary of a type of communication system in which advancements in communication technologies have been implemented. New types of communication services, and effectuation of conventional communication services in improved manners, are possible as a result of implementation of such advancements in communication technologies.
Communication channels defined in a radio communication system are defined upon radio links that extend between the communication stations of the radio communication system. The need to utilize a conventional, wireline connection along the entire communication path extending between sending and receiving stations of the communication system is obviated. For at least a portion of the communication path, a radio link is substituted for the wireline connection. And, when the radio link is substituted for the wireline connection, the need otherwise to utilize a wireline connection along that portion of the communication path is obviated.
A radio communication system provides various advantages. Initial installation and initial deployment of a radio communication system is performed generally in a less costly manner than the corresponding costs required to install and deploy a wireline counterpart. Also, a radio communication system is permitting of implementation as a mobile communication system. In a mobile communication system, one or more of the communication stations operable therein is mobile, i.e., is permitted movement.
A cellular communication system is a type of mobile communication system. Cellular communication systems have achieved high levels of usage and the network infrastructures of cellular communication systems have been installed to encompass significant portions of the populated areas of the world. Voice, and other data, services are effectuated through the use of a cellular communication system.
A cellular communication system is constructed, generally, to be in conformity with a standard, operational specification promulgated by a standards-creating body, such as the EIA/TIA. Successive generations of communication standards have been promulgated, and communication systems have been implemented to be in operational conformity therewith. First-generation, second-generation, third-generation, and successor-generation operational specifications have been promulgated or are under discussion.
Several of the operational specifications set forth CDMA (code-division, multiple-access) communication schemes, utilizing spread-spectrum communication techniques. The IS-95, IS-98, and IS-2000 operational specifications set forth the operational parameters of communication systems that utilize CDMA communication schemes. Other operational specifications set forth the operating parameters of communication systems that utilize other communication schemes, such as TDMA (time-division, multiple-access) schemes or conventional analog communication schemes.
Communication stations operable in a cellular communication system pursuant to a communication session must be in synchronization with one another so that the data that is communicated therebetween is successfully received. A delay lock loop circuit, forming part of a receiver, is sometimes used by which to place, and maintain, the receiver in synchronization with the transmitter. Such circuits are used in spread-spectrum systems as well as other cellular, and other radio, communication systems. Delay lock loop circuits, for instance, are used in communication systems operable pursuant to an IEEE 802.11 standard, the aforementioned IS-95/IS-2000 standards, and a WCDMA standard. In an IS-95/IS-2000 system, the receiver utilizes a pilot signal broadcast during operation of such a communication system, to place the receiver in synchronization with a transmitter.
A delay lock loop circuit generally has two operating modes. A first mode, referred to as an acquisition mode, is first used during initial synchronization when the initial timing between the transmitter and receiver is only coarsely known. In this mode, the delay lock loop circuit attempts to align the receiver and transmitter in a quick manner. Thereafter, a second mode, referred to as a tracking mode, is used. In the tracking mode, the timing of the receiver is close to the correct timing epoch. And, when in the tracking mode, the delay lock loop further reduces timing errors between the receiver and transmitter.
When in the acquisition mode, the timing error is maintained with some known variance, which is dependent upon loop parameters. The amount of variance is traded-off against a desired pull-in time. When in the tracking mode, there no longer is a pull-in requirement, and the loop bandwidth of the delay lock loop circuit is changed in order to provide a tracking error that exhibits a smaller variance.
Conventionally, the architecture of the delay lock loop circuit used for the acquisition mode and the delay lock loop circuit used for the tracking mode use different loop filters.
Conventional delay lock loop circuits, however, are input signal-dependent. That is to say, the delay lock loop circuit is inherently dependent upon the input signal level of input signals applied thereto. And, thus, the circuit is constructed to be capable to receive a range of input signal levels, and circuit-construction compromises are made at other signal levels. Normalization of input signal values is sometimes required and, when the input signal is beyond the accepted range of input signal levels, the delay lock loop circuit might not perform acceptably.
Therefore, an improved manner by which to place, and maintain, a receiver in synchronization with a transmitter is required.
It is light of this background information related to delay lock loop circuits that the significant improvements of the present invention have evolved.
The present invention, accordingly, advantageously provides apparatus, and an associated method, by which to synchronize a receiver to a transmitter operable in a radio communication system, such as a cellular communication system that utilizes a spread-spectrum communication scheme.
Through operation of an embodiment of the present invention, a manner is provided for the receiver that synchronizes the receiver to a signal transmitted to the receiver by the transmitter.
In one aspect of the present invention, a delay lock loop (DLL) circuit is alternately configured to be operated in an acquisition mode and in a tracking mode. The same circuit elements are used irrespective in which of the modes that the delay lock loop circuit is operated.
In another aspect of the present invention, a delay lock loop circuit is provided that is amplitude-independent of an input signal applied thereto. The delay lock loop circuit operates in a deterministic manner to synchronize a receiver to place, and maintain, the receiver in synchronization with a transmitter that transmits a receive signal to the receiver. Irrespective of the signal levels of the receive signal, and the input signal representative thereof, applied to the delay lock loop circuit, the delay lock loop circuit is able to make use of the input signal to perform synchronization operations. Input signal normalization is not required for operation of the delay lock loop circuit, and simplified circuit construction of the delay lock loop circuit is permitted.
In another aspect of the present invention, a sampled representation of an input signal applied to the delay lock loop circuit is utilized to form a feedback signal that alters subsequent operation of a sample generator. Mathematical difference values are formed of symbol values, delayed by positive and negative time offsets. The values of the mathematical differences are integrated over a selected period, down-sampled, hard-limited, and filtered. Filtering of the hard-limited values is effectuated by a filter that exhibits a filter transfer function and is of a selected bandwidth.
Sampled symbol values of zero offsets are filtered by a filter that exhibits a filter transfer function and a filter bandwidth. Once filtered, the sampled symbol values of the zero offsets are used to phase-correct the sampled symbol values of the positive and negative offsets.
The sampled symbol values of the zero offset, the positive offset, and the negative offset are integrated over selected sample periods.
In another aspect of the present invention, a selector operates to select values of selectable parameters of circuit elements of the delay lock loop circuit. The selection of the parameters is dependent upon in which operational mode that the delay lock loop circuit is operated. When in the acquisition mode, the selector selects a first set of parameters by which the circuit elements of the delay lock loop circuit are caused to be operated. And, when in the tracking mode, the selector causes a second set of parameters to be used by which to operate the circuit elements of the delay lock loop circuit. Through suitable selection of the parameter values of the circuit elements, the delay lock loop circuit is caused to operate in either the acquisition mode or the tracking mode. And, the delay lock loop circuit is able to act upon input signals of any amplitude. Normalization of the input signal is not required, and, additionally, circuit simplification is provided.
In these and other aspects, therefore, a delay lock loop circuit, and an associated method, is provided for a receiver. The receiver is operable to receive a receive signal transmitted thereto during operation of a radio communication system. Synchronization of the receiver with the receive signal transmitted thereto is provided. A sample selection signal generator is adapted to receive sampled representations of the receive signal. The sample selection signal generator generates a sample-selection signal. The sample-selection signal is calculated over a selected sampling period. The sample-selection signal is of a value responsive to the sampled representations of the receive signal over selected sample period lengths. Each sampled representation is represented in terms of a positive offset, a negative offset, and a zero offset. A selector is coupled to the sampled selection signal generator. The selector selects operation of the sample selection signal generator, alternately in a first a mode and in at least a second mode. When operation in the first mode is selected, the selector selects the selected sampling period to be of first sample period lengths. And, when operation in the second mode is selected, the selector selects the selected sampling period to be of second sample period lengths.
A more complete appreciation of the present invention and the scope thereof can be obtained from the accompanying drawings that are briefly summarized below, the following detailed description of the presently-preferred embodiments of the invention, and the appended claims.